Transient free high speed coil activation circuit and method for determining inductance of an inductor system

Abstract

The inductors in a switched resonant circuit are alternately connected in make before break fashion to ensure that at least one inductor is always connected to the tank circuit. This avoids switching discontinuities caused by signal propagation delay. By connecting both coils together between individual coil reading cycles, transients are absorbed.

What is claimed is: 
     
       1. A method of indicating the inductance of a system of inductors including a first inductor and a second inductor, comprising: coupling said first inductor to a tank circuit and causing said tank circuit to oscillate at a first resonant frequency determined at least in part by the inductance of said first inductor;   producing a first waveform having a property determined by said first resonant frequency;   coupling said second inductor to said tank circuit without decoupling said first inductor from said tank circuit;   decoupling said first inductor from said tank circuit without decoupling said second inductor from said tank circuit and causing said tank circuit to oscillate at a second resonant frequency determined at least in part by the inductance of said second inductor;   producing a second waveform having a property determined by said second resonant frequency;   whereby said property of said first waveform determined by resonant frequency and said property of said second waveform determined by resonant frequency are indicative of the inductance of said system, namely said property of said first waveform corresponding to the inductance of the first inductor and said property of said second waveform corresponding to the inductance of the second inductor.   
     
     
       2. The method of claim 1 wherein said step of coupling said second inductor to said tank circuit occurs in response to said first waveform. 
     
     
       3. The method of claim 1 wherein said step of decoupling said first inductor from said tank circuit occurs in response to said first waveform. 
     
     
       4. The method of claim 1 wherein said first waveform comprises a variable duty cycle pulse. 
     
     
       5. The method of claim 1 wherein said second waveform comprises a variable duty cycle pulse. 
     
     
       6. The method of claim 1 wherein said step of causing said tank circuit to oscillate at a first resonant frequency is performed by supplying energy to said tank circuit while said first inductor is coupled to said tank circuit. 
     
     
       7. The method of claim 1 wherein said step of causing said tank circuit to oscillate at a second resonant frequency is performed by supplying energy to said tank circuit while said second inductor is coupled to said tank circuit. 
     
     
       8. The method of claim 1 wherein said step of causing said tank circuit to oscillate at a second resonant frequency is performed by supplying energy to said tank circuit while said first inductor is coupled to said tank circuit and continuing to supply energy to said tank circuit while said second inductor is coupled to said tank circuit. 
     
     
       9. The method of claim 1 wherein said step of causing said tank circuit to oscillate at a second resonant frequency is performed by supplying energy to said tank circuit while said first inductor is coupled to said tank circuit, continuing to supply energy to said tank circuit when said second inductor is coupled to said tank circuit and further continuing to supply energy to said tank circuit after said first inductor is decoupled from said tank circuit.